Cardiac surgery was initially undertaken using highly invasive open procedures. A sternotomy, which is a type of incision in the center of the chest that separates the sternum was typically employed to allow access to the heart. In the past several decades, more and more cardiac operations are performed using intravascular or percutaneous techniques, where access to inner organs or other tissue is gained via a catheter.
Intravascular or percutaneous surgeries benefit patients by reducing surgery risk, complications and recovery time. However, the use of intravascular or percutaneous technologies also raises some particular challenges. Medical devices used in intravascular or percutaneous surgery need to be deployed via catheter systems which significantly increase the complexity of the device structure. As well, doctors do not have direct visual contact with the medical devices once the devices are positioned within the body.
One example of where intravascular or percutaneous medical techniques have been employed is in the treatment of a heart disorder called atrial fibrillation. Atrial fibrillation is a disorder in which spurious electrical signals cause an irregular heartbeat. Atrial fibrillation has been treated with open heart methods using a technique known as the “Cox-Maze procedure”. During this procedure, physicians create specific patterns of lesions in the left or right atria to block various paths taken by the spurious electrical signals. Such lesions were originally created using incisions, but are now typically created by ablating the tissue with various techniques including radio-frequency (RF) energy, microwave energy, laser energy, and cryogenic techniques. The procedure is performed with a high success rate under the direct vision that is provided in open procedures, but is relatively complex to perform intravascularly or percutaneously because of the difficulty in creating lesions with the desired characteristics. Various problems may occur if the lesions are incorrectly formed. For example, unless the formed lesions are transmural (e.g., extend fully throughout a thickness of the target cardiac tissue), their ability to block paths taken within the heart by spurious electrical signals may be compromised. In some cases, increased levels of ablative energy, increased delivery times of the ablative energy, or both may allow for lesion transmurality to be achieved in the target cardiac tissue. However, since tissue thickness is variable and may not be easily or readily ascertained in percutaneous procedures, various tissue structures that underlie the target cardiac tissue, but which should not be ablated, may be at risk of being subjected to the ablation energy supplied with increased levels or longer durations. One particular undesired complication that may arise is the formation of atrio-esophageal fistulas.
In this regard, there is a need for improved intra-bodily-cavity transducer-based device systems or control mechanisms thereof that can provide improved indications of lesion transmurality, especially during the formation of the lesion.